The present invention relates to a pick-up assembly for use in a record player and, more particularly, to an improved pick-up assembly for use in stereophonic reproduction having a stylus adapted to slidingly engage in a V-shaped information carrier groove formed a record disk, and a pair of moving coils which move or vibrate in a magnetic field according to the vibration of the stylus.
Conventionally, there have been proposed various pick-up assemblies of the above described type. For example, one type of pick-up assembly is disclosed in Japanese Utility Model Publication No. 19879/1965 published on July 12, 1965. This publication discloses a pick-up assembly as shown in FIGS. 1, 2 and 3 of the attached drawings, in which FIG. 1 is a side-sectional view of the pick-up assembly, FIG. 2 is a fragmentary end view of the pick-up coil assembly and FIG. 3 is a fragmentary side sectional view on an enlarged scale. As shown in FIG. 1, the pick-up assembly includes a permanent magnet 101. One end of this magnet 101 which is polarized in one polarity has a piece of yoke 102 extending downwardly therefrom while the other end which is polarized in the other polarity extends adjacent the yoke 102 through a pole piece 103. In this arrangement, a magnetic field is produced in a space between a free end portion of the yoke 102 remove from the permanent magnet 101 and the tip of the pole piece 103 adjacent the yoke 102, as best shown in FIG. 3. Provided in the space between the yoke 102 and the pole piece 103 is an armature 104 supported on the tip of the pole piece 103 through by a damper 109. A cantilever 108 having one end portion flexibly connected to the tip of the pole piece 103 extends through respective openings formed in the damper 109 and the armature 104, and then through an opening 110 formed in the free end portion of the yoke 102. The other end of the cantilever 108 remote from the pole piece 103 extends outwardly from the opening 110 and carries a stylus 107. Provided around the armature 104 are a pair of coils 105 and 106 which are separately wound around the armature and at right angles to each other, as best shown in FIG. 2. The stylus 107, cantilever 108, armature 104 and coils 105 and 106 constitute a vibrating section. The vibration of the stylus 107, caused by and in scanning engagement with the groove of the record disk which is moved relative to the stylus 107, is transmitted to the armature 104 so that an electric current indicative of the information carried in the groove of the record disk is induced in the respective coils 105 and 106. The above described pick-up assembly, however, has the following disadvantages.
(a) During the manufacturing process it is difficult to wind coils 105 and 106 around the armature or coil supporter 104 which is fixedly mounted on the cantilever 108 which carries the stylus 107. Therefore, it is difficult to produce a number of such assemblies in a simple assembly line. Furthermore, because the coils 105 and 106 wound around and on the supporter 104 come in contact with the damper 109, not only is it difficult to connect the damper 109 flatly to the supporter 104, but it is also difficult to position the damper 109 in a proper position between the pole piece 103 and the armature 104.
(b) For the purpose of improving the sensitivity, the armature 104 is made of a magnetic material. However, such magnetic material undesirably increases the effective mass of the vibrating section. Therefore, the reproduction band width is narrowed.
(c) Since the cantilever 108 must extend loosely through the yoke 102, it becomes necessary to form the opening 110 in the yoke 102 and it also becomes necessary to insert the cantilever 108 subsequently through the opening 110 during the manufacturing process. Furthermore, when it becomes necessary to change the stylus, the operation of removing the cantilever out from the opening 110 and again inserting the cantilever into the opening 110 has to be repeated. Therefore, it is not only difficult to manufacture the pick-up assembly described above in a simple assembly line, but also to later exchange the stylus. Moreover, the opening 110 tends to provide an obstacle to a desired or predetermined distribution of the magnetic field produced between the pole piece 103 and the yoke 102.
(d) Since the yoke 102 and the pole piece 103 are located closely adjacent to the surface of the record disk, a magnetic flux produced between the yoke 102 and the pole piece 103 may leak out to a magnetic material located thereabout such as a turn table. Therefore, magnetic attraction between the turn table and the yoke 102 or the pole piece 103 may cause an undesirable change in the contact pressure between the stylus and the record disk. Furthermore, for preventing the yoke 102 or pole piece 103 from magnetically attracting tiny ferrous particles, it becomes necessary to provide a shielding means such as a thin rubber sheet around the assembly or around the yoke 102 and pole piece 103.
Another type of pick-up assembly is disclosed in Japanese Patent Application No. 5677/1971 which was laid open to public inspection on Dec. 1, 1971. This application discloses a pick-up assembly as shown in FIGS. 4 and 5 of the attached drawings, in which FIG. 4 is a side view of the pick-up assembly with a portion broken away, and FIG. 5 is a fragmentary end view of the pick-up assembly. As shown in FIG. 5, a pair of sector-shaped coils 111 and 112, each wound in, are supported by a coil supporter 117 which is fixedly mounted on a cantilever 118 carrying a stylus 116. These coils 111 and 112, supporter 117, cantilever 118 and stylus 116 make up a vibrating section. Effective portions of the coils 111 and 112, that is, arcuate portions 111a and 112a are positioned in spaced relationship between magnets 113 and 114 where a magnetic field is produced. The coils 111 and 112 are vibrated according to the vibration of the stylus 116 so as to generate a current in the coils 111 and 112. The above described pick-up assembly, however, has the following disadvantages.
(e) For the purpose of improving the sensitivity, each of the coils 111 and 112 is so arranged as to position the arcuate position 111a or 112a in the magnetic field where the magnetic flux is densely distributed. However, this arrangement requires the formation of an elongated portion in each of the coils 111 and 112 which is not affected by the magnetic field. Therefore, the size of each of the coils 111 and 112 is comparatively large and thereby increases the effective mass of the vibrating section. The increased mass of the vibrating section causes a reduction in reproduceability at a high frequency range and, at the same time, the mechanical impedance is increased. Therefore, the reproduction frequency range, that is, the range of frequency which the pick-up assembly can reproduce, is narrowed. Furthermore, since the coil portion which is supported by the supporter 17, that is, where it is not affected by the magnetic field, is comparatively long, the coil may not be rigid enough to eliminate undesired resonance. Moreover, since the coils 111 and 112 are located closely adjacent to each other, each of the coils may be influenced by the other coil to such an extent as to cause crosstalk therebetween.
(f) Since the coils 111 and 112 are comparatively large, the wire necessary to make up each of the coils will be comparatively long. Therefore, the resistance of each of the coils will increase to such an extent as to produce undesirable thermal noise or increase an equivalent input impedance to an amplifier to be connected to the pick-up assembly and thereby causing a production of other noises.
(g) Since the coils 111 and 112 are made in sector shape which is not of point symmetry, it is difficult to produce the coils in a simple assembly line and, at the same time, it becomes difficult to mount such coils in a proper position on the supporter 117.